[RFC PATCH] deprecation: don't enable TCG plugins by default on 32 bit hosts
The existing plugins already liberally use host pointer stuffing for
passing user data which will fail when doing 64 bit guests on 32 bit
hosts. We should discourage this by officially deprecating support and
adding another nail to the 32 bit host coffin.
Signed-off-by: Alex Bennée <alex.bennee(a)linaro.org>
---
docs/about/deprecated.rst | 11 +++++++++++
configure | 11 ++++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 88f0f03786..8a4e249717 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -184,6 +184,17 @@ be an effective use of its limited resources, and thus intends to
discontinue
it. Since all recent x86 hardware from the past >10 years is capable of the
64-bit x86 extensions, a corresponding 64-bit OS should be used instead.
+TCG Plugin support not enabled by default on 32-bit hosts (since 9.2)
+'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+
+While it is still possible to enable TCG plugin support for 32-bit
+hosts there are a number of potential pitfalls when instrumenting
+64-bit guests. The plugin APIs typically pass most addresses as
+uint64_t but practices like encoding that address in a host pointer
+for passing as user-data will loose data. As most software analysis
+benefits from having plenty of host memory it seems reasonable to
+encourage users to use 64 bit builds of QEMU for analysis work
+whatever targets they are instrumenting.
System emulator CPUs
--------------------
diff --git a/configure b/configure
index d08b71f14b..8acb311527 100755
--- a/configure
+++ b/configure
@@ -424,6 +424,7 @@ fi
# Note that this case should only have supported host CPUs, not guests.
# Please keep it sorted and synchronized with meson.build's host_arch.
host_arch=
+host_bits=64
linux_arch=
case "$cpu" in
aarch64)
@@ -434,12 +435,14 @@ case "$cpu" in
armv*b|armv*l|arm)
cpu=arm
host_arch=arm
+ host_bits=32
linux_arch=arm
;;
i386|i486|i586|i686)
cpu="i386"
host_arch=i386
+ host_bits=32
linux_arch=x86
CPU_CFLAGS="-m32"
;;
@@ -458,11 +461,13 @@ case "$cpu" in
mips*)
cpu=mips
host_arch=mips
+ host_bits=32
linux_arch=mips
;;
ppc)
host_arch=ppc
+ host_bits=32
linux_arch=powerpc
CPU_CFLAGS="-m32"
;;
@@ -480,11 +485,13 @@ case "$cpu" in
riscv32 | riscv64)
host_arch=riscv
+ host_bits=32
linux_arch=riscv
;;
s390)
linux_arch=s390
+ host_bits=32
CPU_CFLAGS="-m31"
;;
s390x)
@@ -495,6 +502,7 @@ case "$cpu" in
sparc|sun4[cdmuv])
cpu=sparc
+ host_bits=32
CPU_CFLAGS="-m32 -mv8plus -mcpu=ultrasparc"
;;
sparc64)
@@ -505,6 +513,7 @@ case "$cpu" in
x32)
cpu="x86_64"
host_arch=x86_64
+ host_bits=32
linux_arch=x86
CPU_CFLAGS="-mx32"
;;
@@ -1028,7 +1037,7 @@ if test "$static" = "yes" ; then
fi
plugins="no"
fi
-if test "$plugins" != "no"; then
+if test "$plugins" != "no" && test host_bits = 64; then
plugins=yes
subdirs="$subdirs contrib/plugins"
fi
--
2.39.2